1. Field of the Invention
The present invention relates generally to imaging of three-dimensional (“3D”) volume data sets. More particularly, the present invention relates to improved imaging and analysis of physical attributes representing events within 3D volume data sets.
2. Related Art
Many fields of endeavor require the analysis and imaging of 3D volume data sets. For example, in the medical field, a computerized axial tomography (“CAT”) scanner or a magnetic resonance imaging (“MRI”) device is used to produce a picture or diagnostic image of some part of a patient's body. The scanner or MRI device generates a 3D volume data set that needs to be imaged or displayed so that medical personnel can analyze the image and form a diagnosis.
Three-dimensional volume data sets are also used in various fields of endeavor relating to the earth sciences. Seismic sounding is one method for exploring the subsurface geology of the earth. An underground explosion or earthquake excites seismic waves, similar to low frequency sound waves, that travel below the surface of earth and are detected by seismographs. The seismographs record the time of arrival of the seismic waves, both direct and reflected waves. Knowing the time and place of the explosion or earthquake, the time of travel of the waves through the interior can be calculated and used to measure the velocity of the waves in the interior. A similar technique can be used for offshore oil and gas exploration. In offshore exploration, a ship tows a sound source and underwater hydrophones. Low frequency (e.g., 50 Hz) sound waves are generated by, for example, a pneumatic device that works like a balloon burst. The sounds bounce off rock layers below the sea floor and are picked up by the hydrophones. In this manner, subsurface sedimentary structures that trap oil, such as faults, folds, and domes, are “mapped” by the reflected waves. The data is processed to produce 3D volume data sets that include a reflection or seismic amplitude datavalue at specified (x, y, z) locations within a geographic space.
A 3D volume data set is made up of “voxels” or volume elements having x, y, z coordinates. Each voxel has a numeric data value for some measured or calculated physical property, at a given location. A data value may, for instance, be an eight-bit data word which may include 256 possible values. Examples of geological data values include amplitude, phase, frequency, and semblance. Different data values are stored in different 3D volume data sets, wherein each 3D volume data set represents a different data value. In order to analyze certain geological structures referred to as “events”, information from different 3D volume data sets must be interpreted and then used to analyze different events.
One conventional method of displaying multiple 3D volume data sets requires that the voxels be rescaled in order that the data values from each 3D volume data set fit within the 256 data value range for color display which causes a reduction in accuracy of each 3D volume data set. Another conventional method displays each 3D volume data set, however, controls the visual display of each 3D volume data set by adjusting transparency.
In an article written by Jack Lees, in March 1999, published in The Leading Edge, entitled “Constructing Faults from Seed Picks by Voxel Tracking,” two 3D volume data sets, each using only 128 data values of a 256-data value range, are combined in a single display. The display resolution was significantly reduced, thereby limiting the ability to accurately interpret certain events.
Consequently, there is a need in the art for a system and method to visualize one or more 3D volume data sets with improved accuracy and resolution. Those skilled in the art have therefore long sought and will greatly appreciate the present invention which addresses these and other problems. For purposes of describing the present invention, the terms “image” and “visualize” may be interchangeably used.